Most things built in the dry stone method require some digging first . Wall foundations don't need to be dug as deep as shelters or cairns or dry stone blackhouses. Bridge abutments need to be dug deeper than the bottom of the water course they are to go over.
Here in Saanich BC we've had to dig quite deep to get below the creek bed which tumbles down quite a deeply grooved ravine. Lots of stone will have to be laid below grade before we get to height in order to spring off the sides with the signature voussoirs that form the classic arch that supports the main span of the bridge .
